Maybe your newsletter could have teasers on different topics that link to blog posts, or articles that will let you create different funnels for different interests. Then, once you have them in the funnel, you are able to gather metrics on what is important/valuable to your readers.

Bonus points if the blog posts/articles have affiliate links for readers purchases.

Gold star if the blog posts/articles are also "sponsored content". Then you're getting paid for that too.